Tuesday, November 18, 2014

Grafts survive cold snap

    When I woke up this morning the temperature outside had dropped to 6 degrees F (-14 C). For mid-November that's pretty darn cold. When I drove by some of my young pecan grafts today, I noticed some of the leaves were still frozen on the tree (photo at right). These leaves had frozen back on November 4th during our first hard freeze, but when leaves remain on the tree it indicates that those branches had not fully hardened off in preparation for winter before the cold weather hit. With the extreme cold this morning, did my young grafts suffer cold injury?

   To check for winter injury, I took my pocket knife out and cut into the main stem of the graft and peeled back the bark. Winter injury on pecan first appears as brown streaks in the  inner bark. The inner bark of this tree was healthy and green (photo a left). The two small, circular, brown spots you see on the inner bark are wounds caused by insects that feed on the stem last summer. 
    This young graft had several, small-diameter shoots at the top of the tree (see photo above). These shoots had developed in mid-summer as a result of a second flush of vegetative growth. This was also the portion of the tree that was still holding on to its frozen leaves.
    Were these shoots injured by the extreme cold? To check, I cut into the wood for look at the inner bark (photo at left). I found nice green inner bark. At this point in time, this Kanza graft looks in good shape.
   Early this year, I decided to top-work a few Jayhawk pecan trees to some new cultivars. When you graft such large trees, the scions grow extremely fast and tall. Vegetative growth can continue late into early-Fall and that new tender growth can be prone to winter injury. The photo at right is one of the top-worked trees I grafted last spring. The graft union is painted white and the scion grew a healthy five feet in height this past summer. Note that the branches below the graft have lost all their leaves while top of the new graft has leaves frozen in place. I needed to check this graft for cold injury.

   I cut into the stem of the new graft and peeled back the bark. The inner bark was still green and healthy (photo at left). No cold injury here.